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Post subject: 1968 Blackface or Silverface Circuit?
Posted: Tue Feb 28, 2012 8:53 pm
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Forgive me if this has been covered before but I just picked up a 68 Pro Reverb serial number A11407 and I was wondering if there is any definitive way to tell if it has a Blackface or SilverFace circuit without taking the amp apart.

Thanks in advance.


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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Tue Feb 28, 2012 10:19 pm
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Photos?

1967 was the last year of the Blackfaces

http://ampwares.com/amplifiers/fender-b ... ro-reverb/

and 1968 was the first year of teh Silverfaces

http://ampwares.com/amplifiers/fender-s ... ro-reverb/

The schematics have some minor component and voltage differences:

http://ampwares.com/schematics/proreverb_ab668.pdf

http://ampwares.com/schematics/pro_reverb_aa165.pdf

http://ampwares.com/schematics/pro_reverb_aa1069.pdf

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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Tue Feb 28, 2012 11:36 pm
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Also, you can look at the tube chart. Should have the circuit (AB165 for example). Several models of Fender amps carried the "blackface" circuitry into the SF era. Like my 1969 SR, which has the Holy AB763 circuit.

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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Wed Feb 29, 2012 3:25 am
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Wow Bill, those ampware exhibits are great ! Sonen, It's my experience, from working for a collector, that it really depends on the time it was actually built. Unfortunately, that means an examination of the internal workings of the chassis. Sorry, but IMHO there is no getting around the inspection(guessing just doesn't cut it ). Now, if it's just a casual inquiry, then go with the numbers. Art

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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Wed Feb 29, 2012 8:05 am
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Art & Bill, you are both correct. You cannot tell from tube charts. Though my SFSR came with AB763-type circuit and GZ34 rectifier... it may have been reverted sometime in the past.

Sorry, for the mis-information. :(


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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Wed Feb 29, 2012 4:28 pm
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aclempoppi wrote:
Wow Bill, those ampware exhibits are great ! Sonen, It's my experience, from working for a collector, that it really depends on the time it was actually built. Unfortunately, that means an examination of the internal workings of the chassis. Sorry, but IMHO there is no getting around the inspection(guessing just doesn't cut it ). Now, if it's just a casual inquiry, then go with the numbers. Art


Ampwares has got a TON of info on Fender amps. Its my "go to" site. :D

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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Thu Mar 01, 2012 11:00 am
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Thank you for all of the info!! I also receive the private message below that I thought was very helpful:

Every component and subassembly within your amp will have a date code or an actual date on it -- the chassis, the cabinet, the reverb tank, the speakers, etc. As well, many of the components on the chassis proper will be marked with an EIA manufacturer's code. You'll need to remove the chassis from the cab and inspect it for a date code which is usually ink-stamped within, near the underside of the power transformer. If your amp is the original AA165 circuit revision (ie: blackface), most of the wiring will have the cloth push-back insulation. The later silverfaces, beginning in the early summer of 1968, were built with neoprene-insulated wire and marked the start of CBS's "meddling" with the original layout and construction specs. This circuit revision was designated the AB668.


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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Thu Mar 01, 2012 11:17 am
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This little message wouldn't have come from some snowbird state, would it? As solid information you'll ever get.

Good luck with your "new" amp!


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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Thu Mar 01, 2012 2:02 pm
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Not sure what state it came from but I do have something to add. I spoke to 2 different techs today (at different shops) that both said the one way to tell 100% for sure if your 68-69 amp is a silverface is to pull the chassis and look for 2 white colored rectangular blocks next to the power tubes. If the amp has them then it is definitely a silverface circuit. If it does not then it could be either a blackface or silverface and further investigation would be necessary. Mine unfortunately has the blocks and is a silverface. I may take it in and have it "blackfaced". Have any of you guys had this work done?


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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Fri Mar 02, 2012 1:54 am
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Sonen, If I can offer a suggestion, don't jump the gun! Let your tech make an inspection. In the past years, it's hard to say which components may have been replaced. As far as "blackfacing" the amp goes, it's only necessary if your ear is that discerning. As long as the power tubes can be matched up close enough, and you are happy with the sound-It's Golden! Art

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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Fri Mar 02, 2012 9:57 am
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Check this link out,it has some good info regarding the circuit differences...btw I own a '66 BF Pro Reverb,it's a great amp,I'm sure yours sounds great too,enjoy it and don't let somebody "mod" it very much!
http://fenderguru.com/amps/pro-reverb


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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Fri Mar 02, 2012 12:07 pm
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Just a little FYI, prior to back dating. The AB668 circuit and the AA165 circuit have more than a few difference between the two. If you like the tone of the amp, as is... and it seems to hold a stable bias. Not overheat. It maybe better to let sleeping dogs lie (if you know what I mean). :wink:

Primary differences I see:

1.) Different circuitry (resistors) around the phase inverter (V6).

2.) Different Bias Power supply circuitry

3.) A bias pot in one (AA165) and a balance pot in the other (AB668)

4.) Addition of 2000 pico-farad snubber caps onto the grids of the 6L6GC (AB668)

5.) Different grid-to-ground resistor values tied to the 6L6GC's in the two circuits.

6.) Addition of 150 ohm, 7watt (these are the white "sandbox" resistors the techs were telling you about) cathode-to-ground, cathode-bias resistor on the AB668 circuit.

7.) Addition of 5 mfd/25 VDC non-polar bypass cap to 6L6GC cathode in AB668.

8.) *** Note the dropping resistor values in the AB668 schematic (between D, C, and B in the PS rail) are wrong. Should be the same as the ones listed in the AA165 circuit.

Most all else, including the trannies seem the same. Best to print out each schematic & layout and study the difference and similarities. Since there is more than a few steps involved, unless you are doing this work--- prolly be equally $$$ to have someone revert the circuit back to the original one. So, it's a pretty big decision. If you do decide to revert-- keep all old parts! This really helps in reverting the amp by to original. And a copy of all you or the tech did folded in an envelope and keep in or with the amp.

Good luck!


http://www.webphix.com/schematic%20heav ... _schem.pdf

http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: 1968 Blackface or Silverface Circuit?
Posted: Fri Mar 02, 2012 11:44 pm
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Sonen, the guys have the straight-up advise ! Have the amp checked out and trust your ears, Bro ! Art

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